The present invention generally relates to printer apparatus and methods and more particularly relates to a printer having an interference-free receiver sheet feed path and method of assembling the printer.
A resistive thermal printer typically comprises the following components: a thermal print head having an array of selectively-activated thermal elements that transfer dyes from a dye donor to a dye receiver in an imagewise fashion; a pressure interface or xe2x80x9cnipxe2x80x9d formed between a platen and the print head, which platen and print head sandwich the dye donor and the dye receiver extending through the nip; a first transport mechanism for transporting the dye receiver; a second transport mechanism for transporting the dye donor; and electronics for mechanical and print head control, as well as electronics for control of data path and image processing.
More specifically, the print head commonly provides a print line of individual elements that can be individually heated to thermally transfer dye from a series of sequential color patches of the dye donor to the dye receiver. The dye donor for a color dye thermal printer is normally supplied in rolls of yellow, magenta, cyan, and sometimes black color patches. The dye receiver may be in cut sheets or rolls of paper or transparency. An image is printed by selectively heating the individual elements of the print head to transfer a first dye to the dye receiver. The dye receiver is then repositioned to receive a second color of the image, and the dye donor is positioned to provide a second dye color. These steps are repeated until all colors of the image are printed on the receiver and the completed print is ejected from the printer. In this manner, such dye color thermal printers form a color print by successively printing with a dye donor onto the dye receiver. Moreover, the print head may take any one of several forms including resistive element, resistive ribbon and laser print heads.
As stated hereinabove, the receiver may be in the form of cut sheets. In this case, the cut sheets are stacked one upon the other to define a stack of cut sheets of the receiver. The stack of cut sheets of receiver reside in a receiver sheet supply tray which is received into the printer. The receiver sheets are stacked in the tray such that a xe2x80x9cleadingxe2x80x9d or front edge of each receiver sheet is the first edge that leaves the supply tray during printing and the xe2x80x9ctrailingxe2x80x9d or back edge of each receiver sheet is the last edge to leave the receiver tray. That is, during printing, the leading edge of the receiver sheet to be printed is fed by an appropriate feeding mechanism along a feed path to the print head, whereupon the print head prints the image on the receiver sheet according to the color of the color patch. The receiver sheet is then fed in a reverse fashion by the feeding mechanism along the feed path until the receiver sheet, including the trailing edge, substantially returns to the supply tray. This process is repeated until all dye color patches belonging to the series of sequential color patches are printed onto the receiver sheet, so that a full color image forms on the receiver sheet. The receiver sheet is controllably moved to a precise starting position with respect to the print head by means of a leading edge sensor disposed adjacent the print head for detecting the leading edge of the receiver sheet. Of course, because each receiver sheet has a front edge, the stack of receiver sheets has a front wall or front edge.
However, it has been observed that, as the receiver sheet being printed returns to the supply tray, the trailing edge of the receiver sheet may encounter and abut the front wall or edge of the stack of receiver sheets residing in the supply tray. This is undesirable because the receiver sheet being returned to the supply tray may crumple to xe2x80x9cjamxe2x80x9d, foul, and otherwise form an obstruction in the receiver sheet feed path. This occurrence interferes with proper operation of the printer and may even cause the printer to become inoperable. In this case, the obstruction has to be removed by the operator of the printer. This, in turn, results in printer down-time and receiver wastage, thereby causing increased cost of printer operation. It is therefore desirable to prevent receiver feed path obstruction caused by the trailing edge of the returning receiver sheet abutting the stack of receiver sheets in the supply tray.
Devices for reducing risk of printer xe2x80x9cjamsxe2x80x9d are known. A sheet tray for preventing printer jams is disclosed in U.S. Pat. No. 5,611,526 titled xe2x80x9cCut Sheet Tray Having A Weighted Pivoting Jam Prevention Memberxe2x80x9d issued Mar. 18, 1997, in the name of David J. Cornell and assigned to the assignee of the present invention. The Cornell patent discloses that risk of jams that occur during return of a cut sheet to a position inside of a cut sheet tray as the trailing edge of the sheet moves past the leading edge of the stack of sheets is reduced by having the returning sheet itself move a lever to a position over a jam area when the cut sheet is returning to the tray. The lever has a first position covering the edge of the other cut sheets and a second position removed from the edge of the other cut sheets, whereby to not interfere with sheets being fed from the stack of sheets. An abutment surface on the member is located along the sheet path to move the member between the first and second positions by the force of the cut sheet moving along the path.
Although the Cornell device satisfactorily reduces risk of printer jams, the Cornell device may not completely eliminate jams caused by the trailing edge of the receiver sheet abutting the front edge of the stack of receiver sheets. In this regard, the force of the cut sheet itself must move the lever in order to cover the jam area when the cut sheet returns to the tray. Also, the cut sheet must move the lever in order to uncover the jam area when the cut sheet is fed from the tray. However, weights of receiver sheets vary depending on the type and manufacturing batch of receiver used. For example, receivers having various percentages of rag content will have weights that differ from receivers having all-wood fiber content. In addition, receiver made from synthetic materials, such as in the case of transparencies, have a reduced coefficient of sliding friction, which may affect the ability of the lever to move as desired. Different weights and coefficients of sliding friction of receiver may cause the lever to move at different speeds or maybe not at all.
Thus, there remains a need to provide a printer having an interference-free receiver sheet feed path and method of assembling the printer.
An object of the present invention is to provide a printer having an interference-free receiver sheet feed path and method of assembling the printer, in order to prevent receiver sheet feed path obstruction due to the trailing edge of the returning receiver sheet abutting the stack of receiver sheets in the supply tray.
With this object in view, the present invention resides in a printer having an interference-free receiver sheet feed path, comprising a print head for forming a mark on a movable receiver sheet belonging to a stack of receiver sheets having an edge portion; a cover member disposed relative to the print head and capable of being actuated to cover the edge portion of the stack of receiver sheets; a biasing member coupled to the cover member for biasing the cover member, so that the cover member covers the front edge portion of the stack of sheets to prevent the front edge portion from interfering with movement of the receiver sheet; and an actuator coupled to the cover member for actuating said cover member, so that the cover member uncovers the front edge portion of the stack of sheets to prevent the cover member from interfering with movement of the receiver sheet.
According to an exemplary embodiment of the present invention, the printer includes a print head for printing an image on a receiver sheet having a trailing edge. The receiver sheet belongs to a stack of receiver sheets that reside in a receiver sheet supply tray. A roller engages the receiver sheet for advancing the receiver sheet from the stack of receiver sheets along a receiver sheet feed path extending from the stack of receiver sheets to the print head. The roller also returns the receiver sheet, trailing edge first, to the stack of receiver sheets along the same feed path. A lever, coupled to the supply tray by means of a spring, is also provided. The lever has a cover portion or canopy adapted to cover the front edge of the stack of receiver sheets when acted upon by the spring, so that the trailing edge of the receiver sheet avoids contact with the front edge of the stack of receiver sheets while the receiver sheet returns to the stack of receiver sheets in the supply tray. This, in turn, avoids crumpling of the receiver sheet in the receiver sheet feed path. In this manner, the receiver sheet feed path is interference-free because the trailing edge of the receiver sheet avoids contact with the front edge of the stack of receiver sheets. Moreover, an actuator engages the lever for providing positive actuation of the lever on demand, so that the cover portion of the lever uncovers the front edge of the stack of receiver sheets only while the receiver sheet is fed from the supply tray. The actuator is energized either by movement of the thermal print head, operation of the roller or signal generated by a leading edge sensor. Thus, the cover portion of the lever covers and uncovers the front edge of the stack of receiver sheets independent of weight and coefficient of sliding friction of the receiver sheet.
A feature of the present invention is the provision of a spring-biased lever having a cover portion for covering the front edge of the stack of receiver sheets.
Another feature of the present invention is the provision of an actuator coupled to the lever for actuating the lever in order to uncover the front edge of the stack of receiver sheets.
An advantage of the present invention is that use thereof reduces printer down-time, receiver wastage and thereby reduces cost of printer operation.
These and other objects, features and advantages of the present invention will become apparent to those skilled in the art upon a reading of the following detailed description when taken in conjunction with the drawings wherein there is shown and described illustrative embodiments of the invention.